The present invention relates to a method and apparatus for ad-hoc network communication. More particularly, the present invention relates to a method and apparatus for vehicle-to-vehicle multi-hop broadcast communication.
Ad-hoc networks are becoming more and more popular, both in general as well as in the automotive field. This popularity may be attributed to the ad-hoc network protocols employed being fairly robust, on the one hand, and the required integrated circuit chips being both cheap and small enabling cost-effective and widespread applications.
Applications of ad-hoc networks in the automotive field and communication between vehicles in particular can be generally categorized in two types, namely safety applications and comfort applications.
Comfort applications, as the name suggests, comprise applications that aim at increasing vehicles' passengers comfort. Examples of such applications are navigation aid, indication of points of interest or Internet connection in a vehicle.
Safety applications, on the other hand, aim at increasing the safety of passengers in traffic, for instance by indicating a developing or existing traffic congestion or by enabling avoidance of collisions of vehicles. For example, one of the safety applications is disclosed in Japanese published patent application No. 2005-124014.
Ad hoc networks to be employed in these applications have to meet complex and rather stringent requirements in order to enable fast and reliable information on imminent danger. For instance, safety applications require a very short time delay to ensure the information is received in time. Also, data transmitted via the ad hoc networks should be as simple as possible in order to allow for fast transmission. Furthermore, this application requires every vehicle has to know relative positions and velocities of every other vehicle within its communication range, so that the system can give a respective warning to the driver when another vehicle is on collision course.
Conventional ad-hoc networks certified for automotive, such as Wireless Local Area Networks (WLAN), IEEE 802.11, IEEE 802.15, Dedicated Short Range Communications (DSRC) or Bluetooth typically provide a smaller communication range or a longer time delay than required by safety applications.
In addition, conventional ad-hoc networks certified for automotive of the above type only provide a limited bandwidth, such as 2 Mbps in IEEE 802.11. This bandwidth is not sufficient in safety applications, as illustrated by the following example. On a congested road with one vehicle every 10 meters on 5 lanes in each direction (10 lanes in total), if each vehicle sends out a data packet with 100 Bytes every 100 ms, the required bandwidth adds up to 3.2 Mbps, exceeding the WLAN broadcast data rate of 2 Mbps.
In Kremer W. et al: “Vehicle density and communication load estimation in mobile radio local area networks (MR-LANs)” form Pioneers to the 21st.century. Denver, May 10-13, 1992, Proceedings of the vehicular technology society conference (VTSC), New York, IEEE, US, vol.2 conf.42, 10 May 1992(1992 May 10), pages 698-704, XP010064612, ISBN 0-7803-0673-2, a method for estimating the communication bandwidth which is required for Cooperative Driving when using wireless communication is described. The estimation of the communication rate is done based on the density of vehicles over variety of road patterns and the required communication distance obtained from the distance needed to stop a car.